Method of avoiding a grid clogging, a grid and an air intake implementing such a method

ABSTRACT

The present invention relates to an air intake grid ( 11 ) having a mesh ( 12 ) provided with elongate elements ( 16 ), two adjacent elongate elements ( 16 ) crossing at a node ( 14, 15 ). At least one elongate element ( 16 ) is surrounded by at least one anti-icing member ( 20 ), said anti-icing member ( 20 ) having a downstream portion ( 22 ) matching the shape of said corresponding elongate element ( 16 ) and an elongate upstream portion ( 21 ) that is resilient and that vibrates under the effect of vortices generated by a flow of air ( 30 ) passing through said grid ( 11 ) after ice has become deposited ( 31 ) on said upstream portion ( 21 ).

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of FR 10 02639 filed on Jun. 24,2010, now FR 2,961,789 B1 issued Jul. 20, 2012, the disclosure of whichis incorporated in its entirety by reference herein.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to an air intake grid and in particular toan air intake in an aircraft power plant, the aircraft having a rotarywing, for example.

The technical field of the invention is more particularly restricted tothe field of combating icing on air intake grids.

(2) Description of Related Art

Since rotorcraft need to operate in a variety of environments, includingunder extreme conditions, the turboshaft engine(s) of such a rotorcraftneeds to be protected so as to withstand such conditions.

To feed a rotorcraft turboshaft engine with air, the engine has an airintake, and the air intake is provided with a duct connecting the engineto the outside air. Two types of air intake can be distinguished,namely:

a dynamic air intake that is fed with outside air under the effectfirstly of the forward speed of the aircraft and secondly of the suctiondrawn in by the engine; and

a static air intake that is fed with air solely under the effect of thesuction drawn in by the engine.

In order to avoid the engine ingesting solid bodies that might damageit, e.g. birds, it is common practice to protect an air intake with agrid. Said solid bodies are then blocked by the grid and do not run therisk of penetrating into the engine.

Although effective, that solution presents a drawback under so-called“icing” flying conditions, and this applies more particularly withdynamic air intakes. Under such flying conditions, ice becomes depositedon the grid and closes off the interstices in the grid, partially, oreven totally.

Consequently, the air intake becomes partially, or even totally, closed.The supply of air to the engine is thus reduced, or even eliminated,thereby giving rise to a significant, or even a complete, drop in thepower developed by said engine, which could lead to an incident.

To remedy that, it is possible to envisage using an oversized grid. Fora dynamic air intake having an area through which air penetratesdynamically into the dynamic air intake, the protective grid has firstand second air-passing sections, with the first air-passing sectionfacing the air-passing area, in contrast to the second air-passingsection that does not face said area. The grid can be said to besomewhat like a mushroom cap covering the dynamic air intake.

Thus, only the first air-passing section runs the risk of picking upice. Under icing conditions, the second air-passing section continues toguarantee at least some minimum air flow rate.

It should be observed that aircraft manufacturers have thus devised avariety of devices for protecting the air intake of turboshaft enginesso as to prevent particles of all kinds being ingested by such engines.For example, document FR 2 250 671 discloses a multipurpose air intakecapable both of preventing the turboshaft engine from ingestingparticles and of allowing flight to take place under icing conditions,without suffering significant loss of performance from the engine.

Document U.S. Pat. No. 4,393,650 is remote from the invention since itrelates to a gas turbine having a pointed rotating fairing as opposed toa stationary grid. That rotating fairing has a rigid conical endfollowed by a rotating flexible frustoconical portion for breaking theplates of ice that become deposited on the fairing.

Similarly, document GB 663 194 describes a rotary screen provided withwires that are elongate in a radial direction, said screen co-operatingwith an annular groove that is drained by pipework.

Thus, ice that is deposited on the wires is expelled towards the grooveand then evacuated by the pipework. It is also possible to inject ade-icing fluid onto the wires.

Document U.S. Pat. No. 5,411,224 describes a grid provided with a frontportion and a rear portion, the rear portion having pointed rigidelements for breaking up foreign bodies that might pass through thegrid.

SUMMARY OF THE INVENTION

A particular object of the present invention is thus to propose a methodand an optimized grid for operating under icing conditions.

Thus, the invention provides a method of avoiding clogging of astationary grid of an air intake in icing conditions, the gridcomprising a mesh provided with a plurality of elongate elements, twoadjacent elongate elements crossing at a node, each elongate elementextending in a long direction between a first node and a second node.

The grid then has a conventional mesh. Such a mesh may be obtained usinggrid-type crossed bars for example, each elongate element representing abar segment extending between two nodes, each node representing anintersection between two bars. The bars are sometimes referred to as“wires”.

According to the method, an anti-icing member is placed around at leastone elongate element, the anti-icing member vibrating under the effectof vortices generated by ice being deposited on said anti-icing memberas the incoming air stream passes through the air intake of the engine.

Thus, the invention makes it possible to avoid ice forming on a gridthat is not moving in rotation, contrary to certain teachings.

Surprisingly, it is found that the deposition of ice gives rise to achange in the shape of the assembly comprising the anti-icing member andthe ice.

Under normal conditions, while the grid is passing a flow of air, theair flow splits on contact with each elongate element, therebysimultaneously creating two vortices behind the grid.

In contrast, when flying under icing conditions, ice adheres to theanti-icing member that covers the elongate element, and more preciselyadheres to its portion that is referred to for convenience as itsportion that is “upstream” with reference to the flow direction of theair.

The deposition of ice gives rise to a disturbance that modifies theshape of the assembly comprising the anti-icing member and the ice, bymaking it asymmetrical relative to the flow direction, for example. Thisresults in two vortices being created on either side of the anti-icingmember, no longer simultaneously, but rather in alternation. This offsetin the creation of vortices causes the vibrating member to vibrate, andin particular causes its upstream portion to vibrate.

This vibration breaks the mass of ice on the upstream portion of theanti-icing member. The ice thus separates from the grid.

This method thus makes it possible to prevent the grid becoming clogged.

It should be observed that the physical phenomenon that gives rise tovibration of the anti-icing member is sometimes referred to as“vortex-induced vibration” (VIV).

Furthermore, such a phenomenon gives rise to turbulence downstream fromthe obstacle as constituted by the grid, which turbulence is known underthe term “Karman vortex streets”. Nevertheless, surprisingly, suchturbulence is not harmful insofar as it disappears when the mass of icedetaches from the anti-icing member.

The method is optimized when the upstream portion of the anti-icingmember is made of an elastic material. It should be observed that theupstream portion represents the leading edge of the anti-icing member.

In addition to the method, the invention provides an air intake gridsuitable for implementing the method.

According to the invention, an air intake grid then comprises a meshprovided with elongate elements, two adjacent elongate elements crossingat a node, each elongate element extending in a long direction between afirst node and a second node.

Furthermore, the grid is remarkable in that at least one elongateelement is surrounded by at least one anti-icing member, the anti-icingmember having a downstream portion arranged on the correspondingelongate element, and an elongate and resilient upstream portion thatvibrates under the effect of vortices generated by a flow of air passingthrough the grid as a result of ice depositing on the upstream portion,the downstream portion being downstream from the upstream portionrelative to the flow of air.

The downstream portion presents a profile that does not generate vortexformation in the absence of ice, e.g. by matching the shape of theelongate element.

Thus, the grid has a covering provided with anti-icing members placed onits elongate elements.

In the event of ice becoming deposited on the upstream portion of ananti-icing member, the above-explained phenomenon causes said upstreamportion to vibrate and consequently causes the ice to become detached.

The grid may have one or more of the following characteristics.

For example, an elongate element provided with an anti-icing memberpresents a section that is elliptical, the downstream portion of theanti-icing member having a section that is elliptical.

This guarantees that the anti-icing member remains in a given position.

This characteristic is unusual, since the bars of a grid usually presentsections that are circular.

Furthermore, the upstream and downstream portions of an anti-icingmember are secured to each other. They may be distinct and assembledtogether by any known method, or together they form a one-piece part.

According to another aspect of the invention, the upstream portion ismade of a material selected from the group of elastomers.

In a first embodiment, between two nodes, an elongate element has aplurality of anti-icing members, with spacing separating adjacent pairsof anti-icing members.

In a first variant of this first embodiment, the spacing is empty.

In a second variant of this first embodiment, the spacing includes acover separating two downstream portions of two adjacent anti-icingmembers by surrounding the elongate element between two anti-icingmembers, the cover having the same shape as said elongate element.

An elongate element may then comprise a sequence of an anti-icingmember, a cover, and an anti-icing member, said sequence optionallybeing reproduced several times.

The cover is optionally secured to the adjacent anti-icing members.

In a second embodiment, an elongate element has a single anti-icingmember extending from a first node towards a second node.

It should be observed that it is possible to obtain the second variantof the first embodiment by hollowing out grooves in an elongate elementof the second embodiment.

Furthermore, each elongate element in contact with the air flow passingthrough the grid advantageously includes an anti-icing member.

Finally, the invention provides an air intake having a protective grid,the grid being a grid according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and its advantages appear in greater detail from thefollowing description of embodiments given by way of illustration withreference to the accompanying figures, in which:

FIG. 1 is a diagram showing a grid of a known type;

FIG. 2 is a view of a grid of the invention arranged in an air intakeshown diagrammatically;

FIG. 3 is a view of an elongate element provided with an anti-icingmember;

FIGS. 4 and 5 are sections showing the method implemented;

FIGS. 6 to 8 are diagrams showing a first embodiment; and

FIG. 9 is a diagram showing a second embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Elements present in more than one of the figures are given the samereferences in each of them.

FIG. 1 shows a grid 1 of a known type suitable for protecting an airintake, e.g. of a power plant.

The grid 1 comprises a mesh 2 having orifices 7 defined by first bars 3and second bars 6 that are interlaced, with a first bar 3 and a secondbar 6 crossing at a node 4, 5.

Each bar has a plurality of segments in the form of elongate elements,each elongate element extending between a first node 4 and a second node5. Thus, each mesh of the grid comprises an orifice 7 defined byelongate elements going from one node to another node.

FIG. 1 shows a grid having a square mesh. Other types of mesh may bedevised, such meshes nevertheless being provided with orifices that aredefined by a plurality of elongate elements, each elongate element goingfrom one node of the mesh to another node.

A grid 1 of this type is effective for preventing undue penetration ofsolid particles into an engine, for example.

Nevertheless, under icing conditions, ice may become deposited on theelongate elements and may potentially clog the orifices of the grid.

FIG. 2 shows an air intake 10 of the invention represented by dashedlines.

The air intake 10 is provided with a novel grid 11.

The grid 11 comprises a mesh 12 made up of a plurality of elongateelements 16, each elongate element extending in a long direction D1 froma first node 14 of the mesh to a second node 15. Two adjacent elongateelements 16 thus join at a node.

The mesh may be obtained from crossed bars, each bar comprising asuccession of elongate elements 16.

The mesh 12 that is shown is square in shape, an orifice 17 of the grid11 being defined by four elongate elements 16 connected together by fournodes. Other forms of mesh could be devised without going beyond theambit of the invention.

According to the invention, an anti-icing member 20 is placed around atleast one elongate element 16, the anti-icing member vibrating under theeffect of vortices generated by ice depositing on the anti-icing member20. More precisely, and for reasons of convenience, the term “vibratingunder the effect of vortices generated by a deposit of ice” is used todesignate the establishment of a phenomenon also known as“vortex-induced vibration” that occurs when a mass of ice forms on theelongate element.

Advantageously, each elongate element 16 that is in contact with the airflow 30 passing through the grid includes an anti-icing member 20.

FIG. 3 shows an anti-icing member 20 arranged around an elongate element16 extending from a first node 14 to a second node 15 in a longdirection D1. It should be observed that the long direction D1 is at anon-zero angle of inclination relative to the direction followed by theflow of air 30 passing through the grid, being perpendicular to saidflow of air 30, for example.

The anti-icing member 20 possess an upstream portion 21 provided with aleading edge of the anti-icing member (relative to the air flow 30), anda downstream portion 22 provided with a trailing edge of the anti-icingmember (relative to the air flow 30).

The downstream portion 22 is shaped to match the shape of the elongateelement 16 that it surrounds in the version shown. Nevertheless, thedownstream portion could also possess a streamlined profile so that inthe absence of ice it does not generate turbulence giving rise tovibration of the anti-icing member.

It should be observed that the elongate element 16 may have a section S1that is elliptical, the downstream portion 22 then also having a sectionS2 that is elliptical or faired. This characteristic serves to preventthe anti-icing member turning around the elongate element.

Furthermore, the upstream portion has a profile that forms a tip forcapturing ice. This portion is optionally made of a material selectedfrom the group of elastomers in order to enhance its elasticity. It ispossible to select an elastomer that has a glass transition temperaturethat is low, of the order of −40° C., for example, so as to guaranteethat operation is acceptable over the entire flying range of an aircraftfitted with said grid 11.

With reference to FIG. 3, the upstream portion 21 and the downstreamportion 22 form a single one-piece part, as opposed to constituting twodistinct elements that are secured to each other.

In a variant that is not shown, the upstream portion 21 and thedownstream portion 22 are two distinct parts that are secured to eachother.

It should be observed that independently of the variant, it is possibleto thread the anti-icing member 20 about the elongate element 16 duringfabrication of the grid 11.

By way of example, another technique consists in making a continuouscovering over the trailing edge of the upstream portion so as to be ableto clip the anti-icing member 20 elastically onto the elongate element16.

FIGS. 4 and 5 explain the operation of the invention.

With reference to FIG. 4, in icing conditions, a mass of ice may form onthe grid 11. The upstream portion 21 of an anti-icing member 20 isupstream from the other members of the grid 11, so ice builds up on saidupstream portion 21.

The flow of air 30 passing through the grid then gives rise to vortices100, and more precisely to two vortices 100 that are offset from eachother downstream from each anti-icing member 20.

With reference to FIG. 5, this offset of the vortices 100 drivesvibration of the anti-icing member, and in particular of its upstreamportion 21. The movement of the portion 21 along arrows F breaks up thebuild up of ice, which is then eliminated by being entrained in the flowof air.

No movement of the grid 11 is therefore required to achieve suchbreaking.

In order to encourage breaking, it is possible to envisage heating theelongate elements using conventional means.

FIGS. 6 to 8 show a first embodiment.

In this first embodiment, a plurality of anti-icing members 20 arearranged on a common elongate element 16 between two nodes 14 and 15.

Any two adjacent anti-icing members 20 on a given elongate element 16are then spaced apart by spacing 40.

In a first variant of this first embodiment, as shown in FIG. 6, thespacing 40 is empty.

Conversely, in a second variant of this first embodiment, as shown inFIGS. 7 and 8, the spacing 40 is provided with a cover 41 surroundingthe elongate element between two downstream portions 22 of two adjacentanti-icing members 20 on the same elongate element 16. It can beunderstood that said two downstream portions 22 of two adjacentanti-icing members 20 may be secured to the cover 41 between them.

FIGS. 7 and 8 also show two different variants of the upstream portion21 of the anti-icing members 20. The upstream portion 21 completelycovers the downstream portion 22 of an anti-icing member 20 in the longdirection D1 in the variant of FIG. 7, and covers part of the downstreamportion 22 of an anti-icing member 20 in the long direction D1 in thevariant of FIG. 8.

Finally, in the second embodiment of FIG. 9, the elongate element 16 hasa single anti-icing member 20 extending from a first node 14 to a secondnode 15.

It can be seen that by machining such an anti-icing member, it ispossible to obtain the second variant of the first embodiment.

Naturally, the present invention may be subjected to numerous variationsas to its implementation. Although several embodiments are describedabove, it will readily be understood that it is not conceivable toidentify exhaustively all possible embodiments. It is naturally possibleto envisage replacing any of the means described by equivalent meanswithout going beyond the ambit of the present invention.

What is claimed is:
 1. A method of avoiding clogging of a stationarygrid of an air intake in icing conditions, the method comprising:providing a grid having a mesh with a plurality of elongate elements,including two adjacent elongate elements crossing at a node, eachelongate element extending in a long direction (D1) between a first nodeand a second node; mounting an anti-icing member around at least oneelongate element between the first node and the second node, theanti-icing member having a hollow core with a cross-sectioncorresponding to a cross-section of the at least one elongate element toprevent rotation of the anti-icing member relative to the at least oneelongate element; configuring the anti-icing member to have an upstreamportion that splits airflow generally symmetrically in the absence ofice to create two balanced vortices behind the grid that do not inducevibrations in the anti-icing member; and providing the upstream portionwith a tip for capturing ice, such that the upstream portion splitsairflow asymmetrically in the presence of ice creating two unbalancedvortices, inducing vibrations in the upstream portion under the effectof the unbalanced vortices generated by the ice being deposited on theanti-icing member.
 2. An air intake grid comprising: a mesh providedwith elongate elements, two adjacent elongate elements crossing at anode, a first elongate element extending in a long direction (D1)between a first node and a second node defining a central portionbetween the first node and the second node, the first elongate elementhaving a cross-section; at least one anti-icing member surrounding thecentral portion of the first elongate element, the anti-icing memberhaving a hollow core with a cross-section corresponding to thecross-section of the first elongate element to inhibit rotation relativeto the first elongate element, the anti-icing member further having adownstream portion arranged on the first elongate element in adownstream direction, and an elongate and resilient upstream portionthat splits airflow generally symmetrically in the absence of ice tocreate two balanced vortices behind the grid that do not inducevibrations in the anti-icing member, the upstream portion having a tipconfigured to capture ice, such that the upstream portion splits airflowasymmetrically in the presence of ice creating two unbalanced vorticesinducing vibrations in the upstream portion under the effect of theunbalanced vortices as a result of the ice depositing on the upstreamportion, the downstream portion being downstream from the upstreamportion relative to the flow of air.
 3. A grid according to claim 2,wherein the first elongate element presents a section (S1) that iselliptical, the downstream portion of the anti-icing member having asection (S2) that is elliptical.
 4. A grid according to claim 2, whereinthe upstream portion and the downstream portion together form aone-piece part.
 5. A grid according to claim 2, wherein the upstreamportion is made of a material selected from the group of elastomers. 6.A grid according to claim 2, wherein, between two nodes, the firstelongate element has a plurality of anti-icing members, with spacingseparating adjacent pairs of anti-icing members.
 7. A grid according toclaim 6, wherein the spacing includes a cover matching the shape of thefirst elongate element and separating two downstream portions of twoadjacent anti-icing members.
 8. A grid according to claim 2, wherein thefirst elongate element has a single anti-icing member extending alongthe central portion.
 9. A grid according to claim 2, wherein eachelongate element in contact with the flow of air includes an anti-icingmember.
 10. An air intake provided with a protective grid, wherein thegrid is a grid in accordance with claim
 2. 11. A grid according to claim5, wherein the material selected from the group of elastomers has aglass transition temperature on the order of −40° C.
 12. An air intakegrid comprising: a mesh having a plurality of elongate members includinga first elongate member having a periphery defining a cross section, theplurality of elongate members defining a plurality of nodes at crossingpoints including first and second nodes at respective crossing points onthe first elongate member; and an anti-icing member having a hollow corewith a cross-section corresponding to the cross section of the firstelongate member, the anti-icing member including a first portion securedto the periphery of the first elongate member between the first node andthe second node to prevent rotation of the anti-icing member relative tothe first elongate member, the anti-icing member further including anupstream portion configured to split airflow generally symmetrically inthe absence of ice to create two balanced vortices behind the grid thatdo not induce vibrations in the anti-icing member, the upstream portionhaving a resilient tip at a first end oriented in an upstream directionrelative to a flow of air passing through the grid, the resilient tipbeing configured to capture ice from an air intake, split airflowasymmetrically and generate unbalanced vortices in the flow of air inresponse to captured ice, and induce vibrations in response to thegenerated unbalanced vortices, the anti-icing member further having astreamlined cross-section at a second end oriented in a downstreamdirection relative to the flow of air so that in the absence of ice thesecond end does not generate turbulence giving rise to vibrations in theanti-icing member.
 13. The grid of claim 12, wherein the first elongatemember has an elliptical cross-section normal to a long axis and theanti-icing member has a corresponding elliptical cross-section at asecond end oriented in a downstream direction relative to the flow ofair.
 14. The grid of claim 12, further comprising additional anti-icingmembers arranged about respective members of the plurality of elongatemembers between respective nodes of the plurality of nodes.
 15. The gridof claim 12, wherein the first portion of the anti-icing membersurrounds the first elongate member.
 16. The grid of claim 12, whereinthe anti-icing member has a profile with a line of symmetry that isparallel to a direction of the flow of air.
 17. The grid of claim 12,wherein the anti-icing member is threaded about the one of the pluralityof elongate members.